Waveguide directional coupler

ABSTRACT

A directional coupler for a waveguide comprises two probes penetrating into the waveguide and separated by an interval equal to a quarter of the wavelength corresponding, in the guide, to the operating frequency. The two probes are connected to two ports of a square hybrid, the length of the side of which is equal to a quarter of the wavelength corresponding, in the hybrid, to the above-mentioned frequency. The square hybrid may be detached from the waveguide either through making the probes integral with the hybrid, or through making them the extensions of coaxial jacks integral with the guide, the hybrid being then provided with two mating plugs.

United States Patent 91 Lamy et al.

[ 1March 20, 1973 WAVEGUIDE DIRECTIONAL COUPLER [75] Inventors: Michel Lamy; Jacques Billard, both of Paris, France [30] Foreign Application Priority Data Oct. 13, 1970 France ..7036927 [52] US. Cl ..333/l0, 333/11, 333/21 R, 333/84 M [51] Int. Cl ..H01p 5/12, l-lOlp 5/14, l-lOlp 3/08 [58] Field of Search .....333/l0, 11, 84, 84 M, 98, 97, 333/21; 324/58 R, 58 A, 58 B, 58 C [5 6] References Cited UNITED STATES PATENTS 2,775,737 12/1956 Purcell ..333/l0 X 3,066,264 1 1/1962 Goetter ..333/1 1 X 2,423,390 7/1947 Korman.... 2,609,450 9/1952 Early ..333/l0 Primary Examiner-Herman Karl Saalbach Assistant Examiner-Marvin Nussbaum Attorney-Edwin E. Greigg [5 7] ABSTRACT A directional coupler for a waveguide comprises two probes penetrating into the waveguide and separated by an interval equal to a quarter of the wavelength corresponding, in the guide, to the operating frequency. The two probes are connected to two ports of a square hybrid, the length of the side of which is equal to a quarter of the wavelength corresponding, in the hybrid, to the above-mentioned frequency. The square hybrid may be detached from the waveguide either through making the probes integral with the hybrid, or through making them the extensions of coaxial jacks integral with the guide, the hybrid being then provided with two mating plugs.

1 Claim, 3 Drawing Figures WAVEGUIDE DIRECTIONAL COUPLER The present invention relates to waveguide directional couplers and more particularly to couplers of small size, operating at frequencies of less than l Gc/s.

It is well known to design microwave couplers which are formed essentially by a waveguide section of the same kind as that forming the circuit into which the coupler is to be incorporated, in association with one or two auxiliary waveguide sections perpendicular to, or parallel with, the first mentioned waveguide section, depending upon the desired mode of coupling. In this way, good performance characteristics can readily be obtained but, even when using flat waveguide for the auxiliary sections, these couplers are bulky and constitute a monoblock unit which, if they are an optional element of an equipment, requires the coupler to be substituted by a waveguide section where the equipment is desired without a coupler, which means that a flange connection arrangement has to be provided.

The object of the present invention is to overcome these drawbacks.

In accordance with the invention, there is provided a directional coupler for a waveguide, said coupler comprising two probes penetrating into said waveguide and respectively contained in two planes perpendicular to the direction of propagation of the waves in said waveguide, said two planes being separated by a distance equal to a quarter of the propagation wavelength in said waveguide for the center operating frequency thereof, and a hybrid junction having first and second pairs of ports, said junction being formed by transmission line elements so arranged that the difference between the paths from either of the ports of said second pair of the two ports of the first pair respectively be equal to a quarter of the propagation wavelength in said transmission lines elements for said frequency, said two probes being respectively connected to the two ports of said first pair.

The invention will be better understood and other of its features rendered apparent, from a consideration of the description and the accompanying drawings, in which:

FIG. 1 is a schematic illustration of an embodiment of a directional coupler in accordance with the invention;

FIG. 2 is a sectional view of a practical embodiment of the coupler of FIG. 1; and

FIG. 3 is a sectional view of a variant embodiment of a directional coupler in accordance with the invention.

In FIG. 1, a rectangular waveguide l is shown, the upper broad face of which is provided with two apertures 2 and 3. The centers of those apertures are respectively located in two planes perpendicular to the broad faces of the guide and intersecting the upper broad face along the lines 16 and 17 spaced by a distance D k,,/4, where A, is the propagation wavelength in the guide for the operating mean frequency thereof. Two probes 4 and 5 respectively penetrate into the guide normally to the broad face through the apertures 2 and 3, and are respectively coupled to two adjacent ports of a square hybrid 8. As is known a square hybrid comprises four transmission line sections forming a square, the length of the sides of which is equal to a quarter of the propagation wavelength in those sections for the operating mean frequency thereof.

The four ports are at the four corners of the square.

Preferably the square hybrid of the coupler according to the invention is made of flat transmission line sections, for example three-conductor strip lines, 9 to 12, only the inner conductors of which have been shown in FIG. 1. The probes 2 and 3 are respectively connected to the inner conductors of two adjacent ends 6 and 7 of two parallel line sections, 9 and 11, those ends being two ports of the square hybrid, the opposite ends 13 and 14 of these same sections being the other two ports of the square hybrid and forming two ports of the directional coupler.

The result of this arrangement is that, if a signal is supplied to the. square hybrid 8 through the port 14, the probes 4 and 5 will excite the waveguide l in the direction of the arrow 15, Le. in the direction from 4 to 3. Supply to the hybrid 8 through the port 13 will, of 1 course, produce excitation of the waveguide in the reverse direction.

In the same way, a wave propagating through the waveguide will give rise to the delivery of energy either at the terminal 13 or at the terminal 14 according to the direction of propagation of the wave in the guide.

The depth of penetration of the probes 4 and 5 is of course a function of the desired coefficient of coupling with the waveguide. The position of the apertures 2 and 3, shown here on the center axis of the broad face of the waveguide, may be altered provided that the centre of the apertures 2 and 3 be aligned parallel to this axis. The advantage of offsetting the position of the probes relatively to the center axis (when the desired coefficient of coupling is comparatively low) lies in that, for a given coupling coefficient, the probes will then be longer so that the mechanical tolerance becomes greater as concerns their precise length.

In FIG. 2, where similar references designate similar elements, the inner conductors of the square hybrid 8 are shown inserted between two plates of dielectric material 20 and 21 which themselves are inserted between two metal plates 22 and 23 forming the external conductors of the transmission lines of the square hybrid. The ports 13 and 14 are located behind the junction and are not visible in the figure.

The probes 4 and 5 are integral with the square hybrid, whose attachment to the waveguide 1 simply requires the drilling of two small holes 2 and 3 and the assembly of a mechanical centering and clamping unit which will respectively position and fix the elements while at the same time effecting center necessary electrical contacts.

In the variant embodiment shown in FIG. 3, the probes 4 and 5 are the extensions of the internal conductors of two coaxial jacks 24 and 25 respectively, which are integral with the waveguide 1, the outer conductors of the jacks making contact with the upper broad face of the waveguide. The square hybrid 8 of FIG. 1 is attached to the guide by means of two coaxial plugs (not shown in the drawing) corresponding to the two jacks, the inner conducts of the plugs being respectively connected to the inner conductors of the ports 6 and 7 of the hybrid, and their outer conductors directly making electrical contact with the lower conductors of those ports.

In this arrangement, the electrical operation of the coupler is of course unchanged with respect to what has been described hereinbefore, the slight mechanical complication which results being compensated for by more suitable positioning of the probes since their positioning is then independent of thedetachable square hybrid, the detachment being very simply effected through separating the plugs from the jacks.

Experiments carried out with this kind of coupler were made using a WR 229 waveguide operating in the range between 3.7 and 4.2 Gc/s.

For a given length of penetration of the probes into the waveguide, the coupling variation remained less then percent over the stated frequency band, the standing wave ratio in the waveguide remaining better than 1.02. I

This variation of the coupling as a function of the frequency may be easily tolerated for a number of applications, in particular as concerns the couplers used for measurements, in the latter necessitating anyhow a precise calibration relating the coupling to the frequency.

The use of this coupler, which involves only a slight increase over the waveguide thickness, is particularly relevant to radio relay links where the space available in the racks is reduced.

Of course the invention is not limited to the embodiments which have been described. It will readily be apparent that the square hybrid could be substituted by any hybrid junction made of transmission line elements, and having two pairs of ports such that the difference between the paths from either port of one of said pairs to the other ports of the other pair, respectively, be equal to a quarter of the propagation wavelength in said elements at the center operating frequency. i

What is claimed is:

l. A directional coupler for a waveguide having broad faces, said coupler comprising two probes penetrating into said waveguide through one of said broad faces and respectively contained in two planes perpendicular to the direction of propagation of the waves in said waveguide, said two planes being separated by a distance equal to a quarter of the propagation wavelength in said waveguide for the center operating frequency thereof, and a square hybrid having first and second pairs of ports, said square hybrid being formed by transmission line elements so arranged that the difference between the paths from either of the ports of said second pair to the two ports of the first pair respectively be equal to a quarter of the propagation wavelength in said transmission line elements for said frequency, said two probes being respectively connected to the two ports of said first pair; said transmission line elements being flat conductor lines parallel to said broad faces; said coupler comprising two coaxial plugs mechanically integral with said hybrid, andv two corresponding coaxial jacks having inner conductors, mechanically integral with said waveguide, said probes being extensions of said inner conductors of said jacks. 

1. A directional coupler for a waveguide having broad faces, said coupler comprising two probes penetrating into said waveguide through one of said broad faces and respectively contained in two planes perpendicular to the direction of propagation of the waves in said waveguide, said two planes being separated by a distance equal to a quarter of the propagation wavelength in said waveguide for the center operating frequency thereof, and a square hybrid having first and second pairs of ports, said square hybrid being formed by transmission line elements so arranged that the difference between the paths from either of the ports of said second pair to the two ports of the first pair respectively be equal to a quarter of the propagation wavelength in said transmission line elements for said frequency, said two probes being respectively connected to the two ports of said first pair; said transmission line elements being flat conductor lines parallel to said broad faces; said coupler comprising two coaxial plugs mechanically integral with said hybrid, and two corresponding coaxial jacks having inner conductors, mechanically integral with said waveguide, said probes being extensions of said inner conductors of said jacks. 